With an electrophotographic copying apparatus according to the Carlson process, once the surface of a photosensitive member is electrified, an electrostatic latent image is formed by exposing, thereby the formed electrostatic latent image is developed by a toner, and then, the resultant positive image is transferred and fixed onto a paper sheet or the like. Additionally, the photosensitive member is subjected to removal of remaining toner, electrical neutralizing, and cleaning of the member surface, in order to allow repeatedly used during the course of long service life.
Accordingly, the requirements of an electrophotographic photosensitive member include not only an electrification property, and electrophotographic properties such as smaller dark attenuation, but physical properties in relation to repeated operations, such as a press life, wear-resistance, and moisture-resistance, as well as satisfactory resistance to ozone generated when corona charge is applied, or to ultraviolet ray emitted during exposing (environmental resistance).
A conventional electrophotographic photosensitive member commonly used in the art is an inorganic photosensitive member having a photosensitive layer principally comprising an inorganic photoconductive material such as selenium, zinc oxide, and cadmium sulfide.
Recently, the research and development of various organic photoconductive materials as materials for forming photosensitive layer in an electrophotographic photosensitive member is actively undertaken in the art.
For example, Japanese Patent Examined Publication No. 10496/1975 describes an organic photosensitive member having a photosensitive layer containing poly-N-vinylcarbazole and 2,4,7-trinitro-9-fluorenone. This photosensitive member, however, does not necessarily satisfy the requirements of sensitivity and press life. To solve such a disadvantage, a development effort has focused on an organic photosensitive member with high-sensitivity and longer press life, wherein a photosensitive layer comprises a specific material being capable of generating an electrical charge and another specific material being capable of transporting the generated charge. In forming such a "separated function" type electrophotographic photosensitive member, a specific material intended for one of the two specific functions is arbitrarily selected from a wide range of materials. Accordingly, an electrophotographic photosensitive material having arbitrary properties may be rather readily available.
Diverse types of materials effectively serving as a charge generating material of such a separated function type electrophotographic photosensitive member have been proposed. One example of an inorganic material serving this purpose is an amorphous selenium described in Japanese Patent Examined Publication No. 16198/1968. This material is used together with an organic charge transporting material.
Additionally, may types of electrophotographic photosensitive members comprising an organic dye or organic pigment as a carrier generating material have been proposed. For example, those having a photosensitive material containing a bisazo compound are known in the art by Japanese Patent Open to Public Inspection (hereinafter referred to as Japanese Patent O.P.I. Publication) Nos. 37543/1972, 22834/1980, 79632/1979, and 116040/1981.
Incidentally, known photosensitive members incorporating an organic photoconductive material are usually used for a negative-charging application. This is because a negative-charge application allows a larger hole transporting capacity relative to an electrical potential and is advantageous in terms of photo-sensitivity or the like.
Such a negative-charge application, however, has been found to have the following disadvantages. The first problem is that ozone is readily produced in an environment during negative-electrification by an electrifier, thus deteriorating the environmental condition. The second problem is that development with a negative-charge type photosensitive member requires a positive-polarity toner; and manufacturing a positive-polarity toner is difficult in view of a triboelectrical electrifying array for ferromagnetic charged particles.
Correspondingly, the use of a photosensitive member comprising an organic photoconductive material electrified in positive polarity has been proposed. In the case of a positive-charge type photosensitive member comprising a charge transporting layer disposed on a charge generating layer wherein the charge transporting layer is formed using a material) having a great transporting capability, the charge transporting layer is contains, for example, trinitrofluorenone. This substance, however, is inappropriate as it has carcinogenic activity. Another possibility is a positive-charge type photosensitive member comprising a charge transporting layer of greater hole transporting capacity, disposed thereon, a charge generating layer. This arrangement means an extremely thin charge generating layer disposed to the surface side, and resulting in poor press life. In short, this arrangement does not provide a practical layer constitution.
U.S. Pat. No. 3,615,414 discloses a positive charge type photosensitive member which contains eutectic complex formed by thiapyrylium salt (charge generating material) and polycarbonate (binder resin). Such a known photosensitive member, however, has a disadvantage; greater memory development, and a readily occurring ghost. U.S. Pat. No. 3,357,989 discloses a photosensitive member which contains phthalocyanine. Phthalocyanine, however, is inappropriate in that its property varies depending on a type of crystal configuration, and thus the crystal configuration requires strict control, and that the sensitivity in shortwave region is insufficient and memory development is great. In short, this type of photosensitive material is inappropriate for a copying apparatus which used a light source of visible wavelength region.
Because of these facts, using a photosensitive member comprising an organic photoconductive material allows little possibility of commercial use. Accordingly, this type of photosensitive member has been almost exclusively used for a negative charge application.
The object of the present invention is to provide an organic photoconductive electrophotographic photosensitive material readily used for a positive charge application and having satisfactory sensitivity, while excelling in wear-resistance, ozone-resistance, and press life.